Integrated circuits (ICs), such as microprocessors, continue to increase circuit densities to support higher levels of performance and functionality. The growth in transistor density has resulted in transistors having shorter gate lengths while power supply voltages have not been scaled proportionally. The increase in performance may include an increase in clock speeds and accordingly an increase in the power required to operate the ICs. The increase in power leads to increased temperature of the ICs. The temperature of the ICs needs to be maintained within certain parameters to ensure the IC does not malfunction or burn-out due to overheating. The temperature may be maintained by utilizing cooling systems (e.g., fans). The temperature of the IC should be monitored and the cooling system adjusted based on the temperature of the IC (e.g., air flow increases as the temperature increases). In addition, if the temperature gets to high the IC may be throttled down or off to bring the temperature down.
On chip temperature sensors may be used to monitor the temperature of the IC. Present thermal sensors include diode elements and inverter based oscillators. Diode thermal sensors require large areas and large current source arrays which make the sensor rather large. Oscillator thermal sensors are a strong function of the supply voltage and these voltages are very hard to calibrate in wafer and chip fabrication making this technique impractical for real time measurements.
Using a single thermal sensor measures the temperature of the IC at and near that particular point. The design of ICs may result in certain hot spots on the IC and there may be a fairly large thermal gradient across the die. Accordingly, it is desirable to position a thermal sensor near the hot-spots. However, it may be difficult to find room in the IC for diode thermal sensors. Moreover, the on-chip hot spots cannot be predicted accurately at the early stages of the design. The hot spots may only be known after the floor plan has been designated and there is a substantial amount of gate level real estate already on the die.
Accurate thermal monitoring of the IC, and in particular the hot spots on the IC, is needed to provide information for throttling and fan regulation.